import java.util.Scanner;

/**
   Counts the number of digits with value 7 in the decimal 
   representation of the integer n
*/
public class CountSevens
{
   public static void main(String[] args)
   {
      Scanner in = new Scanner(System.in);
      int n = in.nextInt();
      int count=0;
      // your work here
      while(n!=0) {
         if(n%10==7) {
            count++;
         }
         n/=10;
      }


      System.out.println(count);
   }
}